Electrically-erasable programmable read only memory (E2PROM), silicon oxide nitride oxide silicon (SONOS) and/or metal oxide nitride oxide silicon (MONOS) based embedded non volatile memory technologies mostly require larger chip area, higher voltage operation, and more process mask layers compared to the recent emerging resistive memory (ReRAM) technology. As emerging ReRAM technology is advanced towards robust reliability (endurance and retention) and high performance (speed and power) by a better selection of transition metal oxide and its switching device, it could be a potential candidate to consider an embedded ReRAM implementation into recent nano meter logic technologies, and/or manufacturing deep submicron CMOS production nodes due to its superior scalability.
Compared to silicon on insulator (SOI) based embedded DRAM having high density and fast access time, the embedded ReRAM can be a potential candidate due to a simple cell scalability advantage with only 3-4 extra masks and less process complexity due to self-alignment process.
Resistive memory device, e.g., resistive switching nonvolatile random access memory is formed using memory elements that have two or more stable states with different resistances. Bistable memory has two stable states. A bistable memory element can be placed in a high resistance state (HRS) or a low resistance state (LRS) by application of suitable voltages or currents. Voltage pulses are typically used to switch the memory element from one resistance state to the other. Nondestructive read operations can be performed to ascertain the value of a data bit that is stored in a memory cell.
Resistive switching based on transition metal oxide switching elements formed of metal oxide films has been demonstrated. Although metal oxide films such as these exhibit bistability, the resistance of these films and the ratio of the high-to-low resistance states are often insufficient to be of use within a practical nonvolatile memory device. For instance, the resistance states of the metal oxide film should preferably be significant as compared to that of the system (e.g., the memory device and associated circuitry) so that any change in the resistance state change is perceptible. The variation of the difference in resistive states is related to the resistance of the resistive switching layer. Therefore, a low resistance metal oxide film may not form a reliable nonvolatile memory device. For example, in a nonvolatile memory that has conductive lines formed of a relatively high resistance metal such as tungsten, the resistance of the conductive lines may overwhelm the resistance of the metal oxide resistive switching element. Therefore, the state of the bistable metal oxide resistive switching element may be difficult or impossible to sense.
Therefore, there is a need for a ReRAM design that can meet the design criteria for advanced memory devices.